In an information processing system constructed by connecting information processing devices by using switches, link aggregation (LAG) is used as a redundancy technology for a layer 2. FIG. 24 is a diagram for explaining LAG. In FIG. 24, 4 information processing devices 2 indicated by S#0 to S#3 are connected by 2 switches 90 indicated by Switch#0 and Switch#1.
While the 2 switches 90 are connected by 4 physical links 90a, the 4 physical links 90a are regarded as one logical link in LAG. Since all paths between layer 2 switches (L2 switches) that support LAG are handled as active paths (paths capable of performing communication), the switches are able to effectively utilize paths. Furthermore, failover based on a detour path (backup) is available at the time of cable disconnection, and availability is improved.
Since order reversal of packets occurs, a simple round-robin method (in units of packets) is not appropriate as an algorithm for selecting paths. Usually, a hash value is calculated based on information of packets, such as an internet protocol (IP) address or a media access control (MAC) address, thereby selecting, based on the hash value, a physical link serving as a delivery destination of packets. Since, from this, a traffic is distributed in units of flows, no order inversion occurs. However, it is known that path selection becomes easy to be influenced by unevenness of a traffic for each of flows as the number of physical lines increases.
In LAG, there is a technology in which hash values and priorities of reception packets are held and output destinations of the reception packets are controlled based on the hash values, the priorities, and buffering states of the reception packets, thereby distributing the packets in units of flows without changing the order thereof (see, for example, Japanese Laid-open Patent Publication No. 2012-205048).
There is a technology for extending a band control rate per LAG group to the total rate of physical bands of all links configuring LAG groups even in a case where the LAG groups are formed across line cards (see, for example, Japanese Laid-open Patent Publication No. 2009-200905).
In LAG, there is a problem that if a path is changed in a case where unevenness of a traffic causes congestion to occur in the path, order reversal of packets occurs. The order reversal of packets causes performance deterioration of a transmission control protocol (TCP). Therefore, in a case where the congestion occur, it is desirable to avoid the order reversal of packets due to a detour and to be able to perform efficient detour control.